The idea of a sub-component of millicharged DM has recently received substantial attention because such a species would have interactions with baryons that become stronger as the Universe cools down. This makes it possible to satisfy constraints on DM-baryon interactions from the Cosmic Microwave Background (CMB), while allowing for observable effects at later times. In particular, such interactions are predicted to reduce the temperature of baryons before the beginning of reionization, leading to modifications of the \(21\,\mathrm {cm}\)  signal from neutral hydrogen at redshift 15–20 [1]}, [2]}, [3]}, [4]}, [5]}, [6]}. Indeed, the EDGES experiment has recently claimed evidence for a discrepancy between predictions and observations of the \(21\,\mathrm {cm}\)  absorption profile at cosmic dawn [7]}, and future radio telescopes will provide a wealth of data from this previously unobserved era.
